The present invention relates to encoding and decoding subtitles and, more particularly, to searching for subtitles on a record medium.
Television broadcasting or video reproduction (such as from a video disk) provides subtitles superimposed on the video image. Problematically, the subtitles are permanently combined with the underlying video image and cannot be manipulated at the receiving (or reproducing) end. The subtitles, for example, cannot be searched for information concerning a specific scene occurring in the video image or sound in its corresponding audio track.
Compact Disc Graphics (CD-G) provide some flexibility in searching subtitles because this technique records graphics in the form of subcodes. However, CD-G has a serious disadvantage because this technique is limited to compact disc (CD) applications, which are slow by television standards. That is, the CD-G technique does not lend itself to manipulation of subtitles in real-time television broadcasts or video reproductions.
As will be shown with reference to FIGS. 18A-C and 19, the lead time required to generate a full CD-G screen is grossly inadequate for normal television or video broadcasts. FIG. 18A depicts the CD-G data format in which one frame includes 1 byte of a subcode and 32 bytes of audio channel data, 24 bytes of which are allocated for L and R audio channel data (each channel having 6 samples with 2 bytes per sample) and 8 bytes allocated to an error correction code. The frames are grouped as a block of 98 frames (Frame 0, Frame 1, . . . , Frame 96 and Frame 97) as shown in FIG. 18B and eight of these blocks P,Q,R,S,T,U,V and W are transmitted as shown in FIG. 18C. The subcodes for Frames 0 and 1 in each block are reserved for sync patterns S1, S1, whereas the subcodes for the remaining 96 frames are reserved for various subcode data. The first two blocks P, Q are allocated to search data employed for searching through record tracks, while the remaining 6 blocks R,S,T,U,V and W are available for graphic data.
CD-G transmits each block of 98 frames at a repeating frequency of 75 Hz. Thus, the data transmission rate for 1 block is (75 Hzxc3x9798 bytes)=7.35 kHz, resulting in a subcode bit rate of 7.35 K bytes/s.
The transmission format for transmitting the information present in blocks R,S,T,U,V and W is shown in FIG. 19, wherein each of the 96 frames (2,3, . . . 97) of the 6 blocks (R,S,T,U,V and W) is transmitted as a packet including 6 channels (R to W) of 96 symbols per channel. The packet is further subdivided into 4 packs of 24 symbols apiece (symbol 0 to symbol 23), with each pack storing a CD-G character. It will be appreciated that, a CD-G character is made up of 6xc3x9712 pixels and, therefore, is easily accommodated in each 6xc3x9724 pack. According to the CD-G format, the 6xc3x9712 CD-G character is stored in the six channels of (R,S,T,U,V and W) at symbols 8 to 19 (12 symbols). The remainder of the symbols in each of the packs store information about the character.
Mode information is one example of information stored in the packs and is stored in the first 3 channels (R, S, T) of symbol 0 in each pack. Item information is another example which is stored in the last 3 channels (U, V, W) of symbol 0. A combination of the mode information and the item information defines the mode for the characters stored in the corresponding pack as follows:
An instruction is another example of information stored in the packs and is stored in all of the channels of symbol 1. Corresponding mode, item, parity or additional information for the instruction is stored in all of the channels of symbols 2 to 7. Parity information for all of the data in the channels of symbols 0 to 19 is stored in all of the channels of the last 4 symbols (symbols 20 to 23) of each pack.
As discussed, the CD-G system is slow. The CD-G data is transmitted at a repeating frequency of 75 Hz and, therefore, a packet which contains 4 packs is transmitted at a rate of 300 packs per second (75 Hzxc3x974 packs). That is, with 1 character allocated to the range of 6xc3x9712 pixels, 300 characters can be transmitted in 1 second. However, a CD-G screen is defined as 288 horizontal picture elementsxc3x97192 CD-G vertical picture elements and requires more than twice the 300 characters transmitted in 1 second. The total transmission time for a 288xc3x97192 screen is 2.56 seconds as shown by the following equation:
(288/6)xc3x97(192/12)÷300=2.56 seconds
With the CD-G system, searching for a specific event (such as a scene) would be extremely time consuming because the time to regenerate each screen (2.56 seconds) by itself is extremely long, when it is considered that screens are usually refreshed in tenths of a second. This problem is compounded when hexadecimal codes are used for the characters because each hexadecimal expression requires 4 bits to represent 1 pixel. As a result, 4 times the data described above is transmitted, thereby increasing the transmission rate to 10.24 seconds (4xc3x972.56 seconds). Since each screen requires a sluggish 10.24 seconds for transmission, a continual transmission of screens means that a lag time of 10.24 seconds is experienced when transmitting screens using the CD-G technique.
In one type of system (known as the CAPTAIN system), dot patterns, as well as character codes, represent the subtitles. This system, however, does not appear to be significantly better than the CD-G system and suffers from some of the same disadvantages. That is, both systems lack the capability to search for a specific event efficiently. In addition, these systems do not provide subtitles with sufficient resolution power in displaying the subtitles. The CD-G system designates only 1 bit for each pixel, and this binary pixel data creates undesired aliasing and flicker. The CAPTAIN system, for example, is developed for a 248 (horizontal picture elements) by 192 (vertical picture elements) display, i.e., a low resolution display, and not for high resolution video pictures of 720xc3x97480.
An objective of the invention, therefore, is to provide an encoding method and apparatus for encoding subtitles to be played back exclusively during the trick playback mode, i.e., during fast, slow or reverse playback modes.
Another object of the invention is to provide a computer-readable memory for directing a computer to search the subtitles stored in the memory.
An even further object of the invention is to provide a decoding method and apparatus for decoding the subtitles to be displayed during the trick playback mode.
In accordance with the above objectives, the present invention provides an encoding method and apparatus which encodes a first subtitle to be displayed during the normal playback mode and writes a corresponding first address to the record medium in an area reserved for such addresses. A second subtitle to be displayed in a respective video frame in place of the first subtitle is encoded onto the record medium at a corresponding address in the area reserved for such addresses.
The present invention further provides a computer-readable memory for directing a computer to playback a subtitle to be displayed during a trick playback mode by pointing the computer to addresses of subtitles to be displayed in the trick playback mode.
The present invention further provides a decoding method and apparatus which decodes the subtitles to be displayed exclusively during the trick playback mode by reading out the subtitle from a subtitle address stored on the record medium.